which has been computed in [1]} and we review here. The key observation is that, since \(Q\)  is a vector in \({\mathbb {M}}^{d+2}\)  and the integral should be Lorenz invariant, we can set \(Q=|Q|(1,1,0)\) . Then by using the parametrization (REF ) we can write,
\(\begin{split}\int \mathrm {d}X_i {\rm e}^{2Q_i\cdot X_i}&=\int _0^{\infty }{\mathrm {d}z_i\over z_i}z_i^{-d}\int \mathrm {d}^d x_i\,{\rm e}^{(1+z_i^2+x_i^2)|Q_i|/z}\\&=\pi ^h\int _0^{\infty }{\mathrm {d}z_i\over z_i}(z_i|Q_i|)^{-h}{\rm e}^{(1+z_i^2)|Q_i|/z_i}\\&=\pi ^h\int _0^{\infty }{\mathrm {d}z_i\over z_i}z_i^{-h}{\rm e}^{-z_i+Q_i^2/z_i}\,,\end{split}\) 
